Compound transmission and shift control therefor

ABSTRACT

A compound transmission (10) comprising a main transmission section (12) connected in series with a range type multiple speed auxiliary drive train unit (14) having at least two selectable range type ratios, and a combined shift control unit (56) therefor, is provided.

This is a divisional of copending application Ser. No. 0/311,564 filedon Feb. 16, 1989 and still pending.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a compound transmission comprising amultispeed main transmission section connected in series with amultispeed auxiliary transmission section, preferably of the combinedsplitter and range type, and to a combined shift control devicetherefor. In particular, this invention relates to a shift control unitfor a manually shifted compound transmission comprising a shift fingeroperated shift bar housing assembly for selecting mainsection gearratios, at least one of said mainsection ratios selectable in twodifferent shift bar housing assembly positions, and a control device orswitch for sensing positioning of the shift bar housing assembly in saidtwo positions and for automatically shifting a two-speed range portionof said auxiliary transmission (or multispeed axle or multispeedtransfer case) accordingly.

2. Description of the Prior Art

Compound transmission systems comprising manually shifted multispeedmain transmission sections connected in series with one or moremultispeed auxiliary drivetrain sections, usually of the range, splitteror combined range/splitter type are well known in the prior art. Theauxiliary sections are usually input and/or output auxiliarytransmission sections but may also be multispeed drive axles, transfercases or the like. Examples of such compound systems may be seen byreference to U.S. Pat. Nos. 4,754,655; 3,648,546; 3,799,002; 4,455,883and 4,527,497, the disclosures of which are hereby incorporated byreference.

These transmissions, while well received and widely utilized in manuallyshifted heavy duty vehicles, are not totally satisfactory as a pair ofswitches, in addition to the shift lever, must be manually manipulatedor the double-H control therefor requires extensive transverse shiftlever movement.

Control devices or assemblies for controlling the shifting of both themain transmission and the auxiliary drive train unit by requiring thevehicle operator to manipulate only a shift lever along an extended Htype shift pattern are also known in the prior art as may be seen byreference to U.S Pat. Nos. 3,429,202; 4,455,883; 4,561,325 and4,633,725, the disclosures of which are hereby incorporated byreference.

These prior art controls are not totally satisfactory as extensive shiftlever/shift tower modification is required; sensors and/or controlslocated at the shift tower, and wiring and/or air control lines thereto,is required; relatively complicated structure, such as multiple shiftfingers are required, the controls are not easily adapted for bothdirect and remote control usage and/or an interlock to inhibit, but notprohibit, shifting of the main transmission section until the selectedauxiliary range ratio is fully engaged was not provided.

SUMMARY OF THE INVENTION

In accordance with the present invention, the drawbacks of the prior artare overcome or minimized by the provision of a compound transmissioncomprising a multiple speed main transmission section connected inseries with a multiple speed auxiliary section, preferably including atleast two speed range gearing, one of which range ratios is utilizedwith only one ratio (or two ratios if controlled by the same shift fork)of the mainsection. The shift control for the transmission includes ashift bar housing actuated by a standard shift lever or cross-shaftshift finger and defines two distinct positions for moving the shift barand shift fork associated with the main section ratio or ratioscompounded by the two-speed auxiliary range ratio.

Movement of the shift finger actuated shift bar housing between the twodistinct positions associated with movement of the one shift fork issensed internally of the shift bar housing to actuate devices mounted atthe transmission for shifting of the auxiliary two-speed range section.In one preferred embodiment, a resilient interlock is actuated duringauxiliary section range ratio shift transients to prohibit shifting ofthe mainsection until the range shift in the auxiliary section iscompleted.

Accordingly, it may be seen that a manually shifted compoundtransmission having a two-speed auxiliary range section compounding onlya single or a pair of mainsection ratios is provided having a shiftcontrol unit wherein the compounded mainsection ratio or pair of ratiosmay be selected in either one of two distinct shift bar housingpositions, preferably corresponding to adjacent parallel legs of anextended H-type shift pattern, shifting between the two parallel legsautomatically resulting in shifting of the two-speed auxiliary to theappropriate ratio. The control unit is activated by a standard shiftfinger and is thus suitable for use in either a direct or remote controltransmission system and requires no special modification of the shiftlever, nor sensors or wiring or air controls at the shift leverlocation, for shifting of the two-speed auxiliary range ratio.

This and other objects and advantages of the present invention may beappreciated by reference to the attached drawings taken in connectionwith the description of the preferred embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view, in section, of the compound transmission of thepresent invention;

FIG. 1A is a partial view, in section, of the auxiliary sectioncountershaft gearing of the transmission of FIG. 1;

FIG. 2 is a schematic illustration of the shift pattern and typicalratio steps for the transmission of FIG. 1;

FIG. 3 is a top view of the transmission of the present invention;

FIG. 4 is a top view of the shift bar housing assembly of thetransmission of FIG. 1;

FIG. 5 is a elevational view taken along line 5--5 of FIG. 4;

FIGS. 6,7 and 8 are partial sectional views taken along line 6--6 inFIG. 4 showing selectable operational positions of the shift bar housingassembly;

FIGS. 9 and 10 respectively, are partial sectional views taken alongline 9--9 of FIG. 4 corresponding to the shift bar housing positionsillustrated in FIGS. 6 and 7, respectively; and

FIG. 11 is a partial sectional view of a typical spring biased plungerassembly.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Certain terminology will be used in the following description forconvenience only and will not be limiting. The words "upwardly","downwardly", "rightwardly", and "leftwardly" will designate directionsin the drawings to which reference is made. The words "forward" and"rearward" will refer respectively to the front and rear ends of thetransmission as conventionally mounted in the vehicle, beingrespectfully to the left and right sides of the transmission asillustrated in FIG. 1. The words "inwardly" and "outwardly" will referto directions toward and away from, respectively, the geometric centerof the device and designated parts thereof. Said terminology includesthe words above specifically mentioned, derivatives thereof and words ofsimilar import.

The term "compound transmission" is used to designate a change speed orchange gear transmission having a main transmission section and anauxiliary drive train unit, such as an auxiliary transmission section,connected in series whereby the selected gear reduction in the maintransmission section may be compounded by further selected gearreduction in the auxiliary transmission section. It is understood, thatwhile the preferred embodiment of the present invention utilizes anauxiliary transmission section connected in series with the maintransmission section, the invention is equally applicable to simpletransmissions connected in series with shiftable multispeed devices suchas multispeed transfer cases and/or multispeed rear drive axle systems.The term "upshift" as used herein shall mean the shifting from a lowerspeed gear ratio to a higher speed gear ratio and the term "downshift"as used herein shall mean the shifting from a higher speed gear ratio toa lower speed gear ratio. The terms "low speed gear" or "low gear" asused herein shall designate a gear utilized for relatively lower forwardspeed operation in a transmission, i.e., a set of gears having a higherratio of reduction of output shaft speed relative to the speed of theinput shaft.

Referring now to FIGS. 1-3, the compound transmission 10 is illustrated.Transmission 10 comprises a main transmission section 12 connected inseries with an auxiliary transmission section 14 having both range andsplitter type gearing. Typically, transmission 10 is housed within asingle multipiece housing 16 and includes an input shaft 18 driven by aprime mover such as a diesel engine (not shown) through a selectivelydisengaged, normally engaged, friction master clutch (not shown).

In the main transmission section 12, the input shaft 18 carries an inputgear 20 for driving at least one countershaft assembly 22. Preferably,as is well known in the prior art and as is illustrated in U.S. Pat.Nos. 3,105,395 and 3,335,616, the disclosures of which are herebyincorporated by reference, input gear 20 simultaneously drives aplurality of substantially identical mainsection countershaft assembliesat substantially identical rotational speeds. Each of the mainsectioncountershaft assemblies comprises a mainsection countershaft 24supported by bearings 26 and 28 in housing 16 and is provided withmainsection countershaft gears 30, 32, 34, 36 and 38 fixed thereto. Aplurality of mainsection drive or mainshaft gears 40, 42 and 44 surroundthe transmission mainshaft 46 and are selectively clutchable, one at atime, to the mainshaft 46 for rotation therewith by sliding clutchcollars 48 and 50 as is well known in the art. Clutch collar 48 may alsobe utilized to clutch input gear 20 to the mainshaft 46 to provide adirect drive relationship between the input shaft 18 and the mainshaft46. Preferably, each of the mainsection mainshaft gears encircles themainshaft 46 and is in continuous meshing engagement with and isfloatingly supported by the associated countershaft gear groups, whichmounting means and special advantages resulting therefrom are explainedin greater detail in above-mentioned U.S. Pat. Nos. 3,105,395 and3,335,616. Typically, clutch collars 48 and 50 are axially positioned bymeans of shift forks or yokes 52 and 54, respectively, associated with ashift bar housing assembly 56 to be described in greater detail below.Clutch collars 48 and 50 are, in the preferred embodiment, of the wellknown non-synchronized double acting jaw clutch type.

Main section mainshaft gear 44 is the reverse gear and is in continuousmeshing engagement with countershaft gears 38 by means of conventionalintermediate idler gears 57 (see FIG. 1A). Main section countershaftgear 32 is provided for powering power takeoff devices and the like. Jawclutches 48 and 50 are three-position clutches in that they may bepositioned in a centered axially nondisplaced, nonengaged position asillustrated or in a fully rightwardly engaged or fully leftwardlyengaged position.

Auxiliary transmission section 14 is connected in series with maintransmission section 12 and is of the three-layer, four speed combinedsplitter/range type as illustrated in above-mentioned U.S. Pat. No.4,754,665. Mainshaft 46 extends into the auxiliary section 14 and isjournalled in the inward end of the output shaft 58 which extends fromthe rearward end of the transmission.

Auxiliary transmission section 14 includes, in the preferred embodimentthereof, a plurality of substantially identical auxiliary countershaftassemblies 60 (see FIG. 1A) each comprising an auxiliary countershaft 62supported by bearings 64 and 66 in housing 16 and carrying threeauxiliary section countershaft gears 68, 70 and 72 fixed for rotationtherewith. Auxiliary countershaft gears 68 are constantly meshed withand support auxiliary section splitter gear 74. Auxiliary countershaftgears 70 are constantly meshed with and support auxiliary sectionsplitter/range gear 76 which surrounds the output shaft 58 at the endthereof adjacent the coaxial inner end of mainshaft 46. Auxiliarysection countershaft gears 72 constantly mesh with and support auxiliarysection range gear 78 which surrounds the output shaft 58. Accordingly,auxiliary section countershaft gears 68 and splitter gear 74 define afirst gear layer, auxiliary section countershaft gears 70 andsplitter/range gear 76 define a second gear layer and auxiliary sectioncountershaft gears 72 and range gear 78 define a third layer, or geargroup, of the combined splitter and range type auxiliary transmissionsection 14.

A sliding two-position jaw clutch collar 80 is utilized to selectivelycouple either the splitter gear 74 or the splitter/range gear 76 to themainshaft 46 while a two-position synchronized clutch assembly 82utilized to selectively couple the splitter/range gear 76 or the rangegear 78 to the output shaft 58. The structure and function ofdouble-acting jaw clutch collar 80 is substantially identical to thestructure and function of the sliding clutch collars 48 and 50 utilizedin the main transmission section 12 and the function of double-actingsynchronized clutch assembly 82 is substantially identical to thestructure and function of prior art double-acting synchronized clutchassembly, examples of which may be seen by reference to U.S. Pat. Nos.4,462,489; 4,125,179 and 2,667,955 the disclosures of all of which arehereby incorporated by reference. The synchronized clutch assembly 82illustrated is of the pin-type described in above-mentioned U.S. Pat.No. 4,462,489.

The splitter jaw clutch 80 is a two-position clutch assembly which maybe selectively positioned in the rightwardmost or leftwardmost positionsfor engaging either gear 76 or gear 74, respectively, to the mainshaft46. Splitter jaw clutch 80 is axially positioned by means of a shiftfork 84 controlled by a two-position piston actuator 86 which isoperable by a driver selection switch such as a button or the like onthe shift knob (not shown) as is known in the prior art. Two-positionsynchronized clutch assembly 82 is also a two-position clutch which maybe selectively positioned in either the rightwardmost or leftwardmostpositions thereof for selectively clutching either gear 78 or 76,respectively, to output shaft 58. Clutch assembly 82 is positioned bymeans of a shift fork 88 operated by means of a two-position pistondevice 90, the actuation and control of which will be described ingreater detail below.

As may be seen by reference to FIGS. 1-2, by selectively axiallypositioning both the splitter clutch 80 and the range clutch 82 in theforward and rearward axial positions thereof, four distinct ratios ofmainshaft rotation to output shaft rotation may be provided.Accordingly, auxiliary transmission section 14 is a three layerauxiliary section of the combined range and splitter type providing fourselectable speeds or drive ratios between the input (mainshaft 46) andoutput (output shaft 58) thereof. The mainsection 12 provides a reverseand three potentially selectable forward speeds. However, one of theselectable mainsection forward gear ratios, the low speed gear ratiosassociated with mainshaft gear 42, is not utilized in the high range.Thus, transmission 10 is properly designated as a "(2+1)×(2×2)" typetransmission providing nine or ten selectable forward speeds, dependingupon the desirability and practicality of splitting the low gear ratio.

While clutch 82, the range clutch, should be a synchronized clutch,double acting clutch collar 80, the splitter clutch, is not required tobe synchronized. The shift pattern for shifting transmission 10 isschematically illustrated in FIG. 2. Divisions in the vertical directionat each gear lever position signify splitter shifts while movement inthe horizontal direction from the three/four and five/six leg of the Hpattern to the seven/eight and nine/ten leg of the H pattern signifies ashift from the low range to the high range of the transmission. Asdiscussed above, splitter shifting is accomplished in the usual mannerby means of a vehicle operator actuated splitter button or the like,usually a button located at the shift lever knob while operation of therange clutch shifting assembly is an automatic response to movement ofthe gear shift lever between the central and rightwardmost legs of theshift pattern as illustrated in FIG. 2 and will be described in greaterdetail below. Range shift devices of this general type are known in theprior art and may be seen by reference to above-mentioned U.S. Pat. Nos.3,429,202; 4,455,883; 4,561,325 and 4,663,725.

Referring again to FIG. 2, and assuming that it is desirable that atransmission have generally equal ratio steps, the mainsection ratiosteps should be generally equal, the splitter step should be generallyequal to the square root of the mainsection ratio steps and the rangestep should equal about the mainsection ratio step raised to the N powerwhere N equals the number of mainsection ratio steps occurring in bothranges (i.e., N=2 in the (2+1)×(2×2) transmission 10). Given the desiredideal ratios, gearing to approximate these ratios is selected. In theabove example, the splitter steps are about 33.3% while the range stepis about 316% which is generally suitable for a "2+1" main transmissionsection having about 78% steps as the square root of 1.78 equals about1.33 and 1.78 raised to the second power (i.e. N equals 2) equals about3.16.

Shift control unit or assembly for controlling shifting of the maintransmission section 12 and the range portion, clutch 82, of theauxiliary section 14 of transmission 10 is defined by the shift barhousing assembly 56. Referring to FIGS. 3-5, shift bar housing assembly56 includes a housing 94 which is mountable to the upper openingprovided in transmission housing 16 and which may carry the range clutchactuating piston assembly 96 thereto. Shift bar housing 94 supports afirst shift bar (also called "shift bar" and/or "shift rail") 96 and asecond shift bar 98 for independent axial movement therein. Shift bar 96carries shift fork 54 for axial movement therewith and shift bar 98carries shift fork 52 for axial movement therewith. Shift bar housing 94also supports a control shaft 100 for axial and rotational movementtherein. Shift rails 96 and 98 and control shaft 100 are axially movableabout axes 102, 104 and 106, respectively, which are substantiallyparallel. Alternatively to being axially rotatably movable in housing94, shaft 100 may be fixed to the housing and support a sleeve 100A foraxial and rotational movement thereabout as may be seen by reference toFIGS. 6-8.

The operation of shift bars 96, 98 is standard and consists of movementof shift bar 96 rightwardly and leftwardly, respectively, from theaxially nondisplaced, neutral position indicated in FIG. 1 for engaginggears 40 and 20, respectively, to mainshaft 46 and movement of shift rod98 rightwardly and leftwardly, respectively, for engagement of gears 44and 42, respectively, to mainshaft 46. A standard interlock mechanismindicated generally at 108 is provided to prevent simultaneous movementof shift bars 96 and 98 from the neutral centered positions thereof toprevent engagement of more than one mainshaft gear at a time to themainshaft 46. The shift bar housing 94 is provided with an opening 110therein for receipt of a shift finger (not shown) carried by either astandard direct control shift lever or cross shaft of a remote controlmechanism as is well known in the prior art. The housing 94 is providedwith means such as tapped apertures 112 adjacent the opening 110allowing mounting of a standard shift lever shift tower or remotecontrol mechanism. Control shaft 100 carries a bushing member 114 fixedfor rotational and axial movement therewith. Bushing 114 defines agenerally upwardly facing socket 116 for receipt of the lower end of ashift finger to define a ball and socket type joint therewith.Accordingly, it may be seen that the shift bar housing assembly 56 isequally well suited for both direct and remote control type shifting oftransmission 10.

Fixed for axial and rotational movement with control shaft 100 are apair of shift tab elements 118 and 120 located generally diametricallyopposite one another and here shown as integral with bushing member 114.Shift bar 96 carries fixed for axial movement therewith a block member22 having a generally circumferentially extending slot 124 thereindefined by opposed strike or engagement surfaces 126 and 128 forselective cooperation with the shifting tab member 118. As may be seen,a nondisplaced positions of control shaft 100 and shift bar 96, tab 118will align with and be rotatable through groove 124. Similarly, shiftbar 98 carries a shift block member 130 having a generallycircumferentially extending groove 132 defined by two oppositely facingstrike surfaces 134 and 136 for selective cooperation with the shift tabmember 120.

Block member 122 defines a first axial groove 138 and a second axialgroove 140 extending axially therethrough and interrupting both of thestrike surfaces 126 and 128 defined thereby. Shift block member 130defines an axially extending guide surface or groove 142 andinterrupting both strike surfaces 134 and 136 defined thereby.

Referring to all of the Figures, and to FIG. 6-8 in particular, theoperation of shift bar housing assembly 56 will be described in greaterdetail. For selection of either reverse low, reverse high, first orsecond speed operation of transmission 10, the control shaft 100 isrotated to its most clockwise position as seen in FIG. 8. In thisposition, the bushing 116 will contact the shift block member 122 tolimit further clockwise rotation as is known in the prior art. A springbiased plunger member 144 is provided to give the operator an indicationof having selected the reverse and low speed rail position, the mostleftward leg of the shift pattern as seen in FIG. 2, and to resilientlyurge the transmission out of this position upon release by the operator.In the position shown in FIG. 8, the control shaft 100 may be movedaxially rightwardly or leftwardly, respectively, causing the shift tabmember 118 to engage strike surfaces 126 or 128, respectively, to causeengagement of gears 44 or 42, respectively, to the mainshaft 46 forreverse or low speed operation (first/second speeds), respectively, oftransmission 10. Axial movement of the control shaft 100 and the shiftbar 96 therewith will be guided by the opposite shift tab member 120interaction with the guide surface 142 defined by the shift block member130 carried by the other shift bar 98.

To select engagement of gears 40 or 20 to the mainshaft 46 for operationin the third, fourth, fifth or sixth speed positions of transmission 10,the bushing 114 and control shaft 100 fixed for rotation therewith ispositioned as shown in FIG. 7. The spring biased plunger assemblY 146and a finger member 148 fixed for rotation with the bushing 114,preferably integral therewith, is provided to assist the operator byproviding a verification field that he has properly selected theposition shown in FIG. 7. Briefly, upon initial engagement of theplunger 146 by finger 148 the operator will be assured that the controlshaft 100 is properly rotationally positioned for operation in themiddle leg of the shift pattern illustrated in FIG. 2. Having positionedthe control shaft 100 and bushing 114 as illustrated in FIG. 7,rightward and leftward axial movement, respectively, of the controlshaft 100 will cause the shift tab 120 to engage strike surfaces 134 or136, respectively, to engage either gear 40 or 20 to the mainshaft 46.It is noted, that in the position illustrated in FIG. 7 the oppositeshift tab is 118 is aligned with guide groove 140 defined in the shiftblock 122 to maintain the rotational position of control shaft 100during axial displacement thereof.

To select high range operation of transmission 10, i.e., operation inthe seventh, eighth, nineth or tenth speeds thereof, the control shaft100 and bushing 114 are located in the counterclockwisemost position asillustrated in FIG. 6. In this position, finger 148 will completelydepress the spring biased plunger 146 and will bottom-out thereon givingthe operator a positive indication of correct rotational positioning ofthe control shaft 100. Shift tab member 120 will be engageable witheither strike surface 134 or 136 whereby rightward and leftward axialmovement of control shaft 100 will result in engagement of gears 40 and20 with mainshaft 46 as is discussed above. It is noted that in theposition illustrated in FIG. 6 the tab member 118 will be guided by thegroove 130 defined in the shift block member 122 to maintain the controlshaft 100 in the correct rotational position thereof during axialdisplacements from the centered position thereof.

To accomplish a shifting of the range section of the transmission 10 toachieve high range operation thereof, synchronized clutch assembly mustbe shifted to the leftwardmost position thereof as illustrated inFIG. 1. To accomplish this without requiring the operator to actuate anycontrol device other than the gear lever movements to the rightwardmostleg of the shift pattern as seen in FIG. 2, the range control valveassembly 150 is provided which will be described in greater detailbelow. Briefly, the range control assembly includes a slotted sleevemember 152 fixed for rotation with shaft 100 which sleeve is providedwith a groove 154 extending along only a limited circumferential portionthereof as may be seen by reference to FIGS. 9 and 10. A spring biasedplunger member 156 connected to a master control valve 158 is axiallyaligned with the grooved portion 154 of sleeve 152 for all axialpositions of shaft 100. Briefly, as may be seen by reference to FIG. 9,when the control shaft 100 is rotated to the high range positioncorresponding to FIG. 6, the plunger 156 will be forced radiallyoutwardly causing the master valve 158 to provide a signal to a slavevalve 160 located at piston assembly 90 to shift the shift fork 88leftwardly as is shown while positioning of the control shaft 100 thelow range position corresponding with FIGS. 7 and 8 will cause theplunger 156 to extend further radially inwardly as shown in FIG. 10causing the master valve 158 to signal the slave valve 160 to shift theshift fork rightwardly from the position shown in FIG. 1 to achieve alow range mode of operation.

The shift bar housing assembly 56 is also provided with a spring biaseddetent assembly 162 comprising a spring biased detent ball 164 biasedinwardly to interact with grooves 166, 168 and 170 provided on the shiftrails to maintain the transmission in the centered or axially displacedpositions thereof and to provide a positive feel of having achieved aproperly centered or displaced position. The shift bar housing assembly56 is also provided with a neutral switch device 172 for sensingdisplacement of the control shaft 100 from the axially centered positionthereof and for providing a neutral/not neutral control signal. Briefly,device 172 comprises a spring inwardly biased plunger 174 which willcooperate with ramps and grooves formed on the control shaft 100 toprovide a signal indicative of axial displacement from the axiallycentered nondisplaced position of the control shaft 100.

For proper operation of transmission 10, and specifically to preventburn up of the synchronizing clutches utilized in the double actingrange clutch assembly 82, it is important that a change in the auxiliarysection range ratio not be initiated until the main transmission sectionis in neutral and that the main transmission section remain in neutraluntil the newly selected auxiliary section range ratio is fully engaged.A change in the range section ratio cannot occur unless there is arotational movement of the control shaft 100 between the positionsillustrated in FIGS. 6 and 7 which will not occur unless both of theshift bars 96 and 98 and the control shaft 100 are in the axiallycentered position as illustrated in FIG. 4 wherein the shift tab members118 and 120 are axially aligned with the circumferentially extendinggrooves 124 and 132 defined by the shift block members 122 and 130. Anot neutral signal from device 172 may also be used to preventinitiation of a range shoft until the mainsection 12 is in neutral.

Accordingly, the shift bar housing 56 of the present invention, as isthe case with prior art devices such as the device illustrated inabove-mentioned U.S. Pat. No. 4,561,325, will not initiate a change fromhigh range to low range or visa versa until such time as the maintransmission section is brought to neutral. However, it is alsoimportant to inhibit re-engagement of the main transmission sectionuntil the range shift has been completed. To accomplish this the controlshaft 100 is provided with a ramped groove 178 for cooperation with aresiliently axially compressible plunger member 180 which will be biasedradially inwardly toward shaft 100 by means of a range interlock crossshaft 182 provided with grooves 184 and 186 which will align with thepin 180 when the range clutch is either in the rightwardmost orleftwardmost position thereof and is also provided with a land section190 which will align with the pin 180 when the synchronized clutchassembly 82 is not fully engaged to bias the interlock pin 180 radiallyinwardly. Preferably, to provide an inhibit rather than a prohibit typeinterlock mechanism to allow shifting of the main transmission inemergency situations, the interlock pin member 180 will be resilientlycompressible as is seen in FIG. 11, allowing the operator to overcomethe rang interlock mechanism. Preferably, cross shaft 182 is integralwith the piston member carrying shift fork 88 or is axially fixedthereto.

As an alternative, it has been found that inhibiting/prohibitingmainsection engagement prior to reengagement of the range section isimportant only in an upshift from low range to high range of the rangeclutch 82 and thus only a range-shift interlock may be provided bymodification of the land across shaft 182 as illustrated in the dottedline in FIG. 4.

Accordingly, it may be seen that an improved compound transmission andshift control unit therefor has been provided.

The description of the preferred embodiments of the present invention isby way of example only and various modifications and/or rearrangement ofthe parts are contemplated without departing from the spirit and thescope of the invention as hereinafter claimed.

We claim:
 1. A combined splitter and range type compound change geartransmission (10) comprising a multiple speed main transmission section(12) connected in series with an auxiliary transmission section;saidmain transmission section comprising a transmission housing (16), aninput shaft (18) rotatably supported in said housing and having an inputgear (20) fixed for rotation therewith, a mainsection countershaftassembly (22) rotatably supported in said housing and driven by saidinput shaft, said mainsection countershaft assembly carrying at least afirst (34), second (36) and third (38) mainsection countershaft gearfixed for rotation therewith, a first (40), second (42) and third (44)mainshaft gear surrounding an independently rotatable mainshaft (46),said first mainshaft gear constantly meshed with said first mainsectioncountershaft gear, said second mainshaft gear constantly meshed withsaid second mainsection countershaft gear and said third mainshaft gearconstantly meshed with an idler gear (57) constantly meshed with saidthird mainsection countershaft gear, a first three-position clutchassembly (48) having an axially nondisplaced position for allowingindependent rotation of said mainshaft, input shaft and first mainshaftgear, a first axially displaced position for rotatably coupling saidinput shaft to said mainshaft and a second oppositely axially displacedposition for rotationally coupling said first mainshaft gear to saidmainshaft, a second three-position clutch assembly (50) having anaxially nondisplaced position for allowing independent rotation of saidmainshaft, relative to said second and third mainshaft gears, a firstaxially displaced position for rotationally coupling said secondmainshaft gear to said mainshaft and a second oppositely axiallydisplaced position for rotationally coupling said third mainshaft gearto said mainshaft, a first shift fork (52) for axially positioning saidfirst three-position clutch assembly and a second shift fork (54) foraxially positioning said second three-position clutch assembly; saidauxiliary section comprising an auxiliary section housing (16),auxiliary section input shaft (46) extending into said auxiliary sectionhousing and driven by said mainshaft and an output shaft (58) extendingfrom said auxiliary section housing, said auxiliary transmission sectioncharacterized by: a splitter gear (74), a splitter/range gear (76) and arange gear (78) all generally coaxial with and rotatable relative tosaid auxiliary section input shaft and said output shaft; an auxiliarysection countershaft assembly (60) comprising an auxiliary countershaft(62) rotationally supported in said housing, a first auxiliarycountershaft gear (68) rotationally fixed to said auxiliary countershaftand constantly meshed with said splitter gear, a second auxiliarycountershaft gear (70) rotationally fixed to said auxiliary countershaftand constantly meshed with said splitter/range gear and a thirdauxiliary countershaft gear (72) rotationally fixed to said auxiliarycountershaft and constantly meshed with said range gear; a two-positionsplitter clutch assembly (80) fixed for rotation with said auxiliarysection input shaft and having a first position for coupling saidsplitter gear to said auxiliary section input shaft and a secondposition for coupling said splitter/range gear to said auxiliary sectioninput shaft; a two-position range clutch assembly (82) fixed forrotation with said output shaft and having a first position for couplingsaid splitter/range gear to said output shaft and a second position forcoupling said range gear to said output shaft; and means (86, 90) forindependently positioning each of said splitter clutch assembly andrange clutch assembly in a selected one of the two positions thereof; acontrol assembly comprising a shift bar housing assembly (56) mounted tosaid transmission housing and including first (98) and second (98)parallel shift rods axially movable therein carrying said first (52) andsecond (54) shift forks, respectively, said first shift rod (98)carrying a shift block member (130) having opposed engagement faces(134, 136) for engagement by a manually operated selector member (120)to axially position said first three-position clutch assembly (48), saidshift block member (130) configured such that the selector member (120)can engage the engagement faces thereof (134, 136) in two distinctadjacent operational positions (FIG. 6 and FIG. 7) of said selectormember and cause axial movement of the associated shift rod (98), guidemeans (138, 140) to prevent movement of said selector member betweensaid adjacent operation positions in the axially displaced position ofeither of said shift rods, and switch means (150) activated by movementof said selector member between said first and second operationalpositions for causing the shifting of said range type auxiliarytransmission section.
 2. The transmission of claim 1 wherein saidtransmission and auxiliary section housings are integral.
 3. Thetransmission of claim 2 wherein said auxiliary section input shaftcomprises an extension of said mainshaft.
 4. The transmission of claim 1wherein said control assembly additionally comprises a two-positionoperator actuated switch for controlling shifting of said splitterclutch assembly.
 5. The transmission of claim 2 additionallycomprising:a range interlock assembly (178-190) having a first positionwhen one of said range auxiliary section ratios is engaged and a secondposition when said range auxiliary section is in a shift transient, saidinterlock assembly in said second position inhibiting axial displacementof said main transmission section shift rods from the axially centeredpositions thereof.
 6. The transmission of claim 5 wherein said interlockassembly includes a plunger member (180) resiliently urged intoengagement with a notched shaft (178, 100) in said shift bar housing inthe second position of said interlock assembly.
 7. The transmission ofclaim 6 wherein said interlock plunger is resiliently axiallycompressible (FIG. 11).